Hi Manoj,
Check whether the status of the Custom FM that you have developed is set to active or not.
Try to execute the FM remotely through SM37 to see whether it is getting triggered or not.
Also, please check whether you are using a valid scenario or not for testing the same.
If all the above reasons are fine, check the following three entries are maintained in the table TE835 or not with the Usage of document line item type as ticked
(a) SECREL-Released Cash Security Deposit
(b) SECREQ-New Cash Security Deposit Req.
(c) SECREV-Rev. Csh Security Deposit Req.
Hope it helps...
Thanks,
Amlan